Particular embodiments of the present invention generally relate to power amplifiers. More specifically, particular embodiments of the present invention relate to a power amplifier configured to cancel even harmonic signals.
Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Power amplifiers are configured to amplify the power of a received AC signal, such as an RF signal. Traditional power amplifiers often include a single nMOS transistor or a cascode both with tank loading. FIG. 1 is a simplified schematic of a traditional power amplifier 100 that includes an nMOS transistor 105 coupled between an inductor 110 and ground. Inductor 110 may be coupled to a voltage source Vdd. Inductor 110 may be coupled to a capacitor 115 in a tank configuration for tuning the resonance of power amplifier 100. The nMOS transistor 105 may be in a common source configuration with the gate of the nMOS transistor 105 configured to operate as an input to receive an AC signal and the drain coupled to the output Vout of power amplifier 100. FIG. 2 is a simplified schematic of another traditional power amplifier 200 that may include first and second nMOS transistors 205 and 210 in series between an inductor 215 and ground. Inductor 215 may be coupled to a voltage source Vdd. Inductor 215 may also be coupled to a capacitor 220 in a tank configuration for tuning the resonance of power amplifier 200. The nMOS transistors 205 and 210 may be in a common source, common gate configuration with the gate of nMOS transistor 205 configured to operate as an input to receive an AC signal and a drain of transistor 210 coupled to the output of power amplifier 200.
In traditional power amplifiers, such as power amplifier 100 and 200 described above, there are typically a number of nonlinear components at the drain of the transistor adjacent to the inductor. For example, the even harmonics, and especially the 2nd harmonic, of a received AC signal tend to be fairly large at the drain of the transistor adjacent to the inductor. The averaging DC current from the even harmonics tends to be relatively large and flows in the inductor generating a relatively large amount of heat. As a result of the heat in the inductor, the inductance may change and in a worst case scenario the inductor may catastrophically fail.
Therefore, it would be desirable to provide new power amplifiers that are configured to reduce the nonlinear components and reduce the adverse effects of the nonlinear components in power amplifiers.